Method for reducing pin count of an integrated coil with driver and ionization detection circuit by multiplexing ionization and coil charge current feedback signals

ABSTRACT

In a first preferred embodiment, the present feature of the invention multiplexes both the ionization and driver current feedback signals into one signal, thus reducing cost and making coil packaging easier. The multiplexed signal first outputs the ionization detection signal and then replaces the ionization signal with the charge current feedback signal when the charge command V in  is enabled. In other words, the multiplexed feedback signal outputs the ionization feedback signal and switches to the charge current feedback signal when the charge command V in  is active. In a second preferred embodiment, the present feature of the invention comprises a method and apparatus to multiplex the ignition driver gate signal with both the ignition coil charge current feedback signal and the ionization signal, thus reducing the package pin count by two.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application Ser.Nos. 60/423,163, filed Nov. 1, 2002, and 60/467,660, filed May 2, 2003,the entire disclosure of these applications being considered part of thedisclosure of this application and hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention is related to the field of internal combustion (IC)engine ignition diagnosis systems. More particularly, it is related tothe field of detecting an ionization signal in the combustion chamber ofan IC engine using the ionization signal to monitor ignition parametersand diagnose engine performance.

2. Discussion

The prior art includes a variety of conventional methods for detectingand using ionization current in a combustion chamber of an internalcombustion engine. However, each of the various conventional systemssuffer from a great variety of deficiencies. For example, prior artionization current detection circuits are generally too slow andgenerate a current signal with low signal-to-noise ratio.

It is desirable to minimize the pin count of an integrated package forreduced cost.

SUMMARY OF THE INVENTION

In view of the above, the described features of the present inventiongenerally relate to one or more improved systems, methods and/orapparatuses for detecting and/or using an ionization current in thecombustion chamber of an internal combustion engine.

In one embodiment, the present invention comprises an integratedignition system including an ignition coil which has a primary windingwith a first and a second end and a secondary winding with a first and asecond end. In addition, the integrated ignition system comprises a coildriver circuit having a first end connected to a second end of saidprimary winding, an ionization detection circuit having at least twoinputs and an output, wherein a first input is connected to the secondend of the primary winding, and a second input is connected to the firstend of the secondary winding. Furthermore, the integrated ignitionsystem comprises a switch having at least two inputs and an output,where a first input is connected to the output of the ionizationdetection circuit, a second input is connected to the second end of thecoil driver circuit, whereby the output of the switch is multiplexedbetween an ionization signal and a charge current feedback signal. Inaddition, the integrated ignition system comprises an ignition plugoperably connected between the second end of the secondary winding andground.

In another embodiment, the integrated ignition system comprises anamplifier having an input and an output, where the input is connected tothe output of the switch.

In a further embodiment, the invention comprises a method of detectingan ionization signal and a driver current feedback signal, including thestep of multiplexing the ionization signal and the driver currentfeedback signal.

In another embodiment, the step of multiplexing the ionization signaland the driver current feedback signal comprises the steps of outputtingan ionization signal, enabling a charge command signal, whereby aprimary winding of an ignition coil is charged, outputting a chargecurrent feedback signal while the charge command is enabled, disablingthe charge command, and outputting the ionization signal after thecharge command is disabled.

In a further embodiment, the ionization signal and the charge currentfeedback signal are output on a same output pin.

Further scope and applicability of the present invention will becomeapparent from the following detailed description, claims, and drawings.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given here below, the appended claims, and theaccompanying drawings in which:

FIG. 1 illustrates an ionization feedback and control system;

FIG. 2 is a graph of an ionization signal;

FIG. 3 is a graph that compares the secondary signals and the ionizationsignals;

FIG. 4 is a graph of an ionization signal when the plug is fouled andthe insulator is overheated;

FIG. 5 illustrates the effect of pre-ignition on an ionization signal;

FIG. 6 is a diagnostics flowchart of the steps taken in the presentembodiment of a method of monitoring ignition efficiency;

FIG. 7 is a flowchart of the steps taken in the present embodiment todiagnose the ignition using the ionization signal;

FIG. 8 is an electrical schematic of a circuit for measuring ionizationcurrent in a ion chamber of an internal combustion engine;

FIG. 9 a is a graph of the control signal V_(IN) from the PCM to theIGBT versus

FIG. 9 b is a graph of the current flow I_(PW) through the primarywinding of the coil versus time;

FIG. 9 c illustrates an output voltage signal Vout resulting from anormal combustion event.

FIG. 10 shows a typical setup for an inline four-cylinder engine;

FIG. 11 illustrates the four stroke cycle operation of the modernautomobile

FIG. 12 illustrates the valve train of an engine;

FIG. 13 illustrates the lobes mounted on a camshaft;

FIG. 14 illustrates the push rod valve gear and the overhead camshaft;

FIG. 15 illustrates the four stroke overlap on the engine crankshaft;

FIG. 16 illustrates a production ionization current detection setup;

FIG. 17 illustrates a typical ionization signal;

FIG. 18 illustrates stroke vs. crank angle (in degrees) for afour-cylinder engine's operating cycle;

FIG. 19 illustrates the optimal spark energy level;

FIGS. 20 a-c illustrate dwell timing;

FIG. 21 illustrates spark timing with respect to cylinder pressure;

FIG. 22 illustrates ionization cylinder identification using partialcharge;

FIG. 23 illustrates a sampling method of determining whether a sparkoccurred;

FIG. 24 illustrates an energy integration apparatus to determine whethera spark occurred;

FIG. 25 is a flowchart of the steps taken when determining whether aspark occurred in a cylinder;

FIG. 26 is a flowchart of the steps taken in the energy integrationapparatus for determining whether a spark occurred;

FIG. 27 illustrates all multiple cylinders being sparked at a givenlocation on the crankshaft, where only one cylinder is actually incompression;

FIG. 28 illustrates ionization cylinder identification using sparkduration;

FIG. 29 illustrates an edge based timer with sample and hold circuit;

FIG. 30 is a flowchart of the steps used when determining spark durationusing edge detection;

FIG. 31 illustrates a compare and integrate circuit;

FIG. 32 is a flowchart of the steps taken in the compare and integratecircuit;

FIG. 33 a is a top view of the ignition coil with integrated coil driverand ionization detection circuitry with the circuitry placed on the topof the coil;

FIG. 33 b is a side view of the ignition coil with integrated coildriver and ionization detection circuitry with the circuitry placed onthe top of the coil;

FIG. 34 is a view of the ignition coil with integrated coil driver andionization detection circuitry with the circuitry placed on the side ofthe coil;

FIG. 35 is a diagram of an integrated coil driver and ionizationdetection sub-system;

FIG. 36 a illustrates the charge command V_(in) signal;

FIG. 36 b illustrates the detected ionization voltage;

FIG. 36 c illustrates the ionization voltage multiplexed with the chargecurrent feedback signal;

FIG. 37 shows a diagram of an integrated coil driver and ionizationdetection sub-system

FIG. 38 is a flowchart illustrating the steps of the present embodimentof an integrated coil driver and ionization detection sub-system;

FIG. 39 is a schematic of an ignition coil;

FIG. 40 illustrates the charging of an ignition coil;

FIG. 41 is an ignition coil charging current profile;

FIG. 42 illustrates an ignition coil discharging;

FIG. 43 illustrates an energy storage capacitor being charged from theprimary winding;

FIG. 44 illustrates an energy storage capacitor being charged from thesecondary winding;

FIG. 45 is a schematic diagram of the circuit that provides a regulatedpower supply for in-cylinder ionization detection by harvesting theexcess ignition coil leakage and magnetizing energy;

FIG. 46 illustrates the high voltage capacitor charging;

FIG. 47 illustrates the high voltage capacitor discharging;

FIG. 48 is a flowchart which illustrates the steps taken in the presentembodiment of a circuit that provides a regulated power supply forin-cylinder ionization detection by harvesting excess ignition coilleakage and magnetizing energy;

FIG. 49 shows a diagram of an integrated coil driver and ionizationdetection sub-system which multiplexes ionization and charge current;

FIG. 50 a illustrates the charge gate signal and the differentialcomparison gate signal;

FIG. 50 b illustrates the detected ionization and the charge currentfeedback signals;

FIG. 50 c illustrates the differential ionization signal multiplexedwith the charge current feedback signal;

FIG. 51 is a flowchart disclosing the steps taken with the presentembodiment of the integrated coil driver and ionization detectionsub-system 90 in which package pin count is reduced by two;

FIG. 52 is a logic block diagram of the present invention for the ASIC(ICIS) option;

FIG. 53 is a logic block diagram of the present invention for the SingleElectronics Package option (DICIS);

FIG. 54 is a circuit diagram of a current sink 95;

FIG. 55 is a circuit diagram of an ionization detection circuit using acharge pump as the bias voltage source;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention detects an ionization signal in an enginecombustion chamber from an ionization detection circuit. The system andassociated subsystems described herein use the detected ionizationsignal to monitor ignition parameters, diagnose and improve engineperformance, detect cylinder ID, control air-to-fuel ratio, controlspark retard timing, control minimum timing for best torque timing, andcontrol exhaust gas recirculation, in addition to other featuresdisclosed in the following embodiments. For clarity, it is noted thatmany of the details concerning the method and apparatus for multiplexboth the ionization and driver current feedback signals into one signalaccording to the present invention are described in Section F of thisdetailed description.

This detailed description includes a number of inventive featuresgenerally related to the detection and/or use of an ionization current.The features may be used alone or in combination with other describedfeatures. While one or more of the features are the subject of thepending claims, other features not encompassed by the appended claimsmay be covered by the claims in one or more separate applications filedon even date by or on behalf of the assignee of the present application.

For clarity, each of the features is described in separate sections ofthis detailed description. Section A discloses the use of an ionizationsignal from an ionization detection circuit to monitor ignitionparameters, such as primary charge timing (or time), primary chargeduration, ignition or spark timing, and ignition or spark duration forfuture “smart” ignition system control.

Section B discloses a circuit for measuring ionization current in acombustion chamber of an internal combustion engine in this circuit, theignition current and the ionization current flow in the same directionthrough the secondary winding of the ignition coil and the circuitdetects an ionization signal by applying a bias voltage between a sparkplug gap. Notwithstanding the described preferred circuit, those skilledin the art will appreciate that many of the features of the inventionmay be implemented through other ionization detection circuits ormethodologies without departing from the scope of the appended claims.

Sections C and D generally relate to methods of detecting cylinderidentification using in-cylinder ionization for spark detection. Moreparticularly, Section C discloses a method of detecting cylinderidentification using the spark phase of an ionization signal todetermine the current engine crank cycle, i.e., Cylinder Identificationin which the spark coils are only partially charged (instead of fullycharged) to a predetermined level. When the air in a cylinder iscompressed (cylinder is in the compression stroke), the resistancebetween the spark plug electrodes will increase. The cylinders that failto fire are on the compression stroke because the gas mixture density ishigh enough that the partially charged coils are unable to deliver thevoltage required to break down the resistance at the spark plug gap.Further, Section D discloses methods of detecting cylinderidentification by determining which cylinder is in compression. Thecylinder with the shortest spark duration is in compression. The twomethods used to time this duration are edge detection and integration.

Section E discloses a circuit comprising an ionization detection circuitand a coil driver transistor which are integrated into the on-plugignition coil. By placing the circuit on top of the coil or on the sideof the coil, the connection distance from the circuit to the secondarywinding is minimized. Thus, the circuit is less susceptible to noise.Another advantage is that the placement is easy to assemble.

Section F discloses a method and apparatus to multiplex both theionization and driver current feedback signals into one signal so thatthe ignition coil with integrated driver and ionization circuit has thesame pin count number as the driver on coil design. When integratingboth the ignition driver circuit and ionization detection circuit ontothe ignition coil (as described in Section E), one open issue is to useminimum pin count of the integrated package to cover both integrateddriver and ionization detection circuits for reduced cost. Bymultiplexing the ignition coil charge current feedback signal with theionization signal, package pin count is reduced by one.

Section G discloses a two step method and apparatus for charging anionization detection circuit, as opposed to just one stage, in which anadditional energy storage capacitor is used. The second capacitorreplaces the first capacitor as the primary energy storage device. Thistwo stage method of charging produces a stable 100 volt output at thefirst capacitor. In addition, by using two capacitors or stages, moreenergy is available to the ionization detection circuit.

Section H discloses multiplexing the ignition primary charge gate signalwith both the ionization and the driver current feedback signals so thatthe ignition coil with an integrated driver and an ionization circuit(See Section E) has a pin count number as few as three.

Section J discloses the use of either an ASIC or a single electronicpackage to integrate an IGBT and an ionization detection electronicsinto one silicon device, or into one electronic package respectively.These devices reduce the cost and complexity of an in-cylinderionization detection system by combining like functionality into oneASIC or electronic module easing packaging constraints.

Section K discloses the use of a high voltage charge pump to provide DCbias voltage for measuring ionization current.

Section A: Ignition Diagnosis Using Ionization Signal

This feature utilizes the ionization signal from an ionization detectioncircuit to monitor ignition parameters, such as primary charge timing(or time), primary charge duration, ignition or spark timing, andignition or spark duration for future “smart” ignition system control.In addition, the ionization signal is also used to detect spark plugcarbon fouling, insulator overheating, pre-ignition, as well as a failedionization circuit or ignition coil.

The performance of an engine is heavily dependent upon the performanceof its ignition system, especially at low load and high EGR (exhaust gasrecirculation) conditions. Understanding how the ignition system behavesat various engine conditions is very beneficial to “smart” control ofthe ignition system. Typically, the primary coil of an ignition systemis charged close to a desired amount of energy as a function of engineoperational conditions such as the local mixture A/F (air to fuel)ratio, pressure, temperature, and EGR concentration. The actual chargedenergy of the primary coil and discharged energy of the secondary coilare unknown. This leads to an ignition system that is not robust toparts-to-parts variation, engine aging, engine operational environmentalcharges, etc. To improve the ignition system robustness, a “smart”ignition system that can change its charged energy to match thedischarged energy is desirable. Therefore, the secondary dischargeinformation is very important. Since the breakdown voltage and sparkduration at the discharge moment can be different from cycle to cycle,it is desirable to monitor some of these parameters.

This invention uses the spark plug ionization signal to monitor theprimary charge time (or primary charge timing 146) and primary chargeduration, and also the secondary discharge time and duration to lay thefoundation for “smart” control of the ignition system 110. In addition,this invention also includes using the ionization signal to detect sparkplug malfunction, such as carbon fouling or insulator overheating 197,pre-ignition 190, and a failed ionization circuit or/and ignition coil.

This feature of the invention is generally directed to a subsystem of anignition diagnostics and feedback control system using ionizationcurrent feedback. The relationship of this subsystem to the diagnosticsand control system is shown in FIG. 1 in the top box “Ignition systemdiagnostics”, 140, 150, 146, 160, 170, and 197, which comprises thefollowing ignition parameters: ignition duration 170, charge duration150, warning signal 197, primary charge time 146, ignition timing 160,and pre-charge 140. The four blocks of the ignition diagnostics andfeedback control system using ionization current feedback that aredirected to spark timing 1480 are the CL knock (advance) limit control1450, the closed-loop MBT spark control 1430, 1490 and 1495, CL misfire& partial burn (retard) limit control 1460 and the CL cold start retardlimit control 1000. There are two blocks directed to the fuel trimvector 975, the individual cylinder A/F ratio control 1300 and the WOTA/F ratio optimization 1900. There is one block directed to the desiredEGR rate 1630, the EGR rate optimization 1600. The three other blocksshown in FIG. 1 are an analog signal processing block ASP, an AIDconversion block A/D and a parameter estimation block 1800. Theparameter estimation block is shown outputting knock 1404, MBT 1435 andmisfire 1414 signals. The input to the analog signal processing blockASP is an ionization current 100.

A typical ionization signal 100 versus crank angle is shown in FIG. 2.Note that the signal shown is a voltage that is proportional to thedetected ionization current. Comparing the secondary voltage 120 andcurrent waveforms 130 (FIG. 3), it is clear that the initial rise of theion signal before the sharp change at the ignition time is thepre-charge (or start of charge) of the primary coil 140. See FIG. 2.After the primary coil charge is completed, the signal goes down andrises almost vertically (i.e., a step rise) versus crank angle. Thebreakdown has occurred at the step's rising edge. Spark timing can bedetected based on this point. That is, the ignition or spark time occurswhen the ionization signal has a step rise. This is the ignition orspark time 160. The time difference between the first rise and thestepped rise is the primary charge duration 150. When the arc betweenthe spark gap dies out, the signal declines rapidly and the secondarycurrent 130 due to the spark reaches zero (see FIG. 3). The durationbetween the sharp stepped rising and the subsequent declining representsthe ignition duration 170. Therefore, based on the ionization signal,the primary charge time 146, the primary charge duration 150, theignition timing 160, and the ignition duration 170 can be detected.These parameters can be monitored for every cylinder of the engine foreach engine cycle.

When a spark plug is fouled, or the spark plug insulator is overheated,or the plug itself is temporarily contaminated by fuel spray, theinsulator of the spark plug serves as a conductor. At these conditions,the ionization signal baseline is no longer equal to the bias voltage105. Depending on how badly the plug is fouled and how overheated theinsulator is, the ionization baseline will be elevated 180 (FIG. 4) fromthe bias voltage 105. Meanwhile, part of the ignition energy will leakthrough the fouled plug or the insulator during the primary chargeperiod. Eventually the remaining energy is not enough to jump the sparkgap and a misfire will occur (196) (FIG. 6). For some cases, thebaseline can be so high that it reaches the limit of the ionizationsignal and the signal becomes of little use. Once the baseline iselevated to (or beyond) a certain threshold (e.g., an elevation ofapproximately 20% or 1 volt above the initial baseline), a warningsignal indicating plug fouling or overheating will be sent out 197 (FIG.6).

When pre-ignition occurs in the cylinder, the ionization signal 100 willdetect ions before the ignition happens (190), see FIG. 5 which showspre-ionization due to pre-ignition. One pre-ignition cycle could lead toan even earlier pre-ignition during the next cycle and damage theengine. It is desirable to control the engine to a cooler operatingcondition once the pre-ignition is detected.

In order to detect an open or a shorted ionization circuit, the biasvoltage (105) is sampled far away from the ignition and combustionevents (e.g., 180 degree after the top dead center). If the sampled biasvoltage is below a given threshold (such as 0.5 volt), an openionization circuit or a short to ground fault can be detected 198 (FIG.6); if the bias voltage is greater than a threshold (e.g., 4.5 volts),an ionization circuit that is shorted to the battery shall be declared199 (FIG. 6). The open or short circuit information can then be used todiagnose the condition of the ignition system (see FIGS. 6 and 7).

Section B: Circuit for Measuring Ionization Current

FIG. 8 is a basic electrical schematic of a circuit 10, which representsthe function block (80) of FIG. 35, for measuring ionization current ina combustion chamber of an internal combustion engine. The circuits notshown in FIG. 8, that are shown in FIG. 35, are the bias circuit and theswitch circuit to multiplex the primary charge current. The componentsand configuration of the circuit 10 are described first, followed by adescription of the circuit operation.

First, with regard to the components and configuration of this feature,the circuit 10 includes an ignition coil 12 and an ignition or a sparkplug 14 disposed in a combustion chamber of an internal combustionengine. The ignition coil 12 includes a primary winding 16 and asecondary winding 18. The ignition plug 14 is connected in electricalseries between a first end of the secondary winding 18 and groundpotential. The electrical connections to a second end of the secondarywinding 18 are described further below. A first end of the primarywinding 16 is electrically connected to a positive electrode of abattery 20. A second end of the primary winding 16 is electricallyconnected to the collector terminal of an insulated gate bipolartransistor (IGBT) or other type of transistor or switch 22 and a firstend of a first resistor 24. The base terminal of the IGBT 22 receives acontrol signal, labeled V_(IN) in FIG. 8, from a powertrain controlmodule (PCM) not shown. Control signal V_(IN) gates IGBT 22 on and off.A second resistor 25 is electrically connected in series between theemitter terminal of the IGBT 22 and ground. A second end of the firstresistor 24 is electrically connected to the anode of a first diode 26.

The circuit 10 further includes a capacitor 28. A first end of thecapacitor 28 is electrically connected to the cathode of the first diode26 and a current mirror circuit 30. A second end of the capacitor 28 isgrounded. A first zener diode 32 is electrically connected across or, inother words, in parallel with the capacitor 28 with the cathode of thefirst zener diode 32 electrically connected to the first end of thecapacitor 28 and the anode of the first zener diode 32 electricallyconnected to ground.

The current mirror circuit 30 includes first and second pnp transistors34 and 36 respectively. The pnp transistors 34 and 36 are matchedtransistors. The emitter terminals of the pnp transistors 34 and 36 areelectrically connected to the first end of the capacitor 28. The baseterminals of the pnp transistors 34 and 36 are electrically connected toeach other as well as a first node 38. The collector terminal of thefirst pnp transistor 34 is also electrically connected to the first node38, whereby the collector terminal and the base terminal of the firstpnp transistor 34 are shorted. Thus, the first pnp transistor 34functions as a diode. A third resistor 40 is electrically connected inseries between the collector terminal of the second pnp transistor 36and ground.

A second diode 42 is also included in the circuit 10. The cathode of thesecond diode 42 is electrically connected to the first end of thecapacitor 28 and the emitter terminals of the first and second pnptransistors 34 and 36. The anode of the second diode 42 is electricallyconnected to the first node 38.

The circuit 10 also includes a fourth resistor 44. A first end of thefourth resistor 44 is electrically connected to the first node 38. Asecond end of the fourth resistor 44 is electrically connected thesecond end of the secondary winding 18 (opposite the ignition plug 14)and the cathode of a second zener diode 46. The anode of the secondzener diode 46 is grounded.

Referring now to FIGS. 8 and 9, the operation of the circuit 10 isdescribed. FIG. 9 a is a graph of the control signal V_(IN) from the PCMto the IGBT 22 versus time. FIG. 9 b is a graph of the current flowI_(PW) through the primary winding 16 of the ignition coil 12 versustime. FIG. 9 c is a graph of an output voltage signal from the circuit10 versus time. As mentioned above, the IGBT 22 receives the controlsignal V_(IN) from the PCM to control the timing of 1) the ignition orcombustion and 2) the charging of the capacitor 28. In this circuitconfiguration, the IGBT 22 is operated as a switch having an OFF, ornon-conducting state, and an ON, or conducting state.

Initially, at time=t₀, the capacitor 28 is not fully charged. Thecontrol signal V_(IN) from the PCM is LOW (see FIG. 9 a) therebyoperating the IGBT 22 in the OFF, or non-conducting, state. Primarywinding 16 sees an open circuit and, thus, no current flows through thewinding 16.

At time=t₁, the control signal V_(IN) from the PCM switches from LOW toHIGH (see FIG. 9 a) thereby operating the IGBT 22 in the ON, orconducting, state. Current from the battery 20 begins to flow throughthe primary winding 16 of the ignition coil 12, the conducting IGBT 22,and the second resistor 25 to ground. Any of a number of switches orswitching mechanisms can be used to connect current through the primarywinding 16. In a preferred embodiment IGBT 22 is used. Between time=t₁,and time=t₂, the primary winding current I_(PW), (illustrated in FIG. 8with a dotted line) begins to rise. The time period between time=t₁ andtime=t₂ is approximately one millisecond which varies with the type ofignition coil used.

At time=t₂, the control signal V_(IN) from the PCM switches from HIGH toLOW (see FIG. 9 a) thereby operating the IGBT 22 in the OFF, ornon-conducting, state. As the IGBT 22 is switched OFF, flyback voltagefrom the primary winding 16 of the ignition coil 12 begins to quicklycharge the capacitor 28 up to the required bias voltage. Between time=t₂and time=t₃, the voltage at the first end of the secondary winding 18connected to the spark plug 14 rises to the voltage level at which theignition begins. The time period between time=t₂ and time=t₃ isapproximately ten microseconds. The first resistor 24 is used to limitthe charge current to the capacitor 28. The resistance value of thefirst resistor 24 is selected to ensure that the capacitor 28 is fullycharged when the flyback voltage is greater that the zener diode.

At time=t₃, an ignition voltage from the secondary winding 18 of theignition coil 12 is applied to the ignition plug 14 and ignition begins.Between time=t₃ and time=t₄, combustion of the air/fuel mixture beginsand an ignition current I_(IGN) (illustrated in FIG. 8 with a dash-dotline) flows through the second Zener diode 46, the secondary winding 18of the ignition coil 12, and the ignition plug 14 to ground. At time=t₄,the ignition is completed and the combustion of the air/fuel mixturecontinues.

At time=t₅, the combustion process continues and the charged capacitor28 applies a bias voltage across the electrodes of the ignition plug 14producing an ionization current I_(ION) due to the ions produced by thecombustion process which flows from the capacitor 28. The current mirrorcircuit 30 produces an isolated mirror current I_(MIRROR) identical tothe ionization current I_(ION). A bias current I_(BIAS) (illustrated inFIG. 8 with a phantom or long dash-short dash-short dash line) whichflows from the capacitor 28 to the second node 48 is equal to the sum ofthe ionization current I_(ION) and the isolated mirror currentI_(MIRROR) (i.e., I_(BIAS)=I_(ION)+I_(MIRROR))

The ionization current I_(ION) (illustrated in FIG. 8 with a dashedline) flows from the second node 48 through the first pnp transistor 34,the first node 38, the fourth resistor 44, the secondary winding 18 ofthe ignition coil 12, and the ignition plug 14 to ground. In thismanner, the charged capacitor 28 is used as a power source to apply abias voltage, of approximately 80 volts, across the spark plug 14 togenerate the ionization current I_(ION). The bias voltage is applied tothe spark plug 14 through the secondary winding 18 and the fourthresistor 44. The secondary winding induction, the fourth resistor 44,and the effective capacitance of the ignition coil limit the ionizationcurrent bandwidth. Accordingly, the resistance value of the fourthresistor 44 is selected to maximize ionization signal bandwidth,optimize the frequency response, and also limit the ionization current.In one embodiment of the present invention, the fourth resistor 44 has aresistance value of 330 k ohms resulting in an ionization currentbandwidth of up to twenty kilohertz.

The current mirror circuit 30 is used to isolate the detected ionizationcurrent I_(ION) and the output circuit. The isolated mirror currentI_(MIRROR) (illustrated in FIG. 8 with a dash-dot-dot line) is equal toor, in other words, a mirror of the ionization current I_(ION). Theisolated mirror current I_(MIRROR) flows from the second node 48 throughthe second pnp transistor 36 and the third resistor 40 to ground. Toproduce a isolated mirror current signal I_(MIRROR) which is identicallyproportional to the ionization current I_(ION), the first and second pnptransistors 34 and 36 must be matched, i.e., have the identicalelectronic characteristics. One way to achieve such identicalcharacteristics is to use two transistors residing on the same piece ofsilicon. The isolated mirror current signal I_(MIRROR) is typically lessthan 300 microamps. The third resistor 40 converts the isolated mirrorcurrent signal I_(MIRROR) into a corresponding output voltage signalwhich is labeled as V_(OUT) in FIG. 8. The resistance value of the thirdresistor 40 is selected to adjust the magnitude of the output voltagesignal V_(OUT). The second diode 42 protects the mirror transistors 34and 36 by biasing on and providing a path to ground if the voltage atnode 38 crosses a threshold. A third transistor can also be used toprotect the mirror transistor.

FIG. 9 c illustrates an output voltage signal V_(OUT) resulting from anormal combustion event. The portion of the output voltage signalV_(OUT) from time=t₅ and beyond can be used as diagnostic informationregarding combustion performance. To determine the combustionperformance for the entire engine, the ionization current in one or morecombustion chambers of the engine can be measured by one or morecircuits 10 respectively.

In the present circuit 10, the ignition current I_(IGN) and theionization current I_(ION) flow in the same direction through thesecondary winding 18 of the ignition coil 12. As a result, theinitiation or, in other words, the flow of the ionization current aswell as the detection of the ionization current is quick. In the presentcircuit 10, the charged capacitor 28 operates as a power source. Thusthe circuit 10 is passive or, in other words, does not require adedicated power source. The charged capacitor 28 provides a relativelyhigh bias voltage from both ionization detection and the current mirrorcircuit 30. As a result, the magnitude of the mirrored, isolated currentsignal I_(MIRROR) is large and, thus, the signal-to-noise ratio is high.

Section C: A Method of Detecting Cylinder ID Using In-CylinderIonization for Spark Detention Following Partial Coil Charging

Current cylinder identification (ID) detection schemes using in-cylinderionization detection have a number of issues: Noise, Vibration andHarshness (NVH) problems when combusting on the exhaust stroke,cold-start hydrocarbon (HC) emissions problems, and delay due to fuelpuddling effects at cold temperatures.

This feature relates to a vehicle that has an internal combustion enginewith at least two cylinders, a spark plug with an electrode gap, and anin-cylinder measurement of ionization level that does not use thecamshaft sensor for variable cam timing.

Numerous prior art systems relate generally to ionization current, butmost deal with detection of misfire and knock, and control of enginevariables such as EGR and spark placement, or circuitry.

Some prior publications deal directly with detecting cylinder ID fromionization current. For example, U.S. Pat. No. 5,563,515A1 usesmisfiring cylinders to detect the cylinder.

Further, U.S. Pat. No. 6,029,631A1 describes a method that uses thevoltage level produced across the spark gap to determine the cylinderID. As discussed below, this method has a number of drawbacks.

The vast majority of automobile internal combustion engines are of thereciprocating piston driven type. The reciprocating engine is a machinethat converts fuel energy to a rotating motion, which is commonlymeasured as horsepower. In the engine, gasoline is added to the air asit passes through the carburetor (or fuel injectors) on its way to thecylinder. This mixture is then burned in the cylinder, which generatesheat, which creates pressure. This pressure pushes the piston down inthe cylinder to turn the crankshaft. FIG. 10 shows a typical setup foran inline four-cylinder automobile engine.

The vast majority of modern automobile engines use a four stroke orcycle operation (see FIG. 11). As the piston starts down on the intakestroke, the intake valve opens and the air/fuel mixture is drawn intothe cylinder (similar to drawing back the plunger on a hypodermic needleto allow fluid to be drawn into the chamber.) When the piston reachesthe bottom of the intake stroke, the intake valve closes, trapping theair/fuel mixture in the cylinder.

In the compression stroke the piston moves up and compresses the trappedair/fuel mixture that was brought in by the intake stroke. The amountthat the mixture is compressed is determined by the compression ratio ofthe engine. The compression ratio on the average engine is in the rangeof 8:1 to 10:1. This means that when the piston reaches the top of thecylinder, the air/fuel mixture is squeezed to about one tenth of itsoriginal volume.

In the power stroke, the spark plug fires, igniting the compressedair/fuel mixture that produces a powerful expansion of the vapor. Thecombustion process pushes the piston down the cylinder with a greatenough force to turn the crankshaft to provide the power to propel thevehicle. Each piston fires at a different time, determined by the enginefiring order. By the time the crankshaft completes two revolutions, eachcylinder in the engine will have gone through one power stroke.

In the exhaust stroke, with the piston at the bottom of the cylinder,the exhaust valve opens to allow the burned exhaust gas to be expelledto the exhaust system. Since the cylinder contains so much pressure,when the valve opens, the gas is expelled with a violent force (that iswhy a vehicle without a muffler sounds so loud.) The piston travels upto the top of the cylinder pushing all the exhaust out before closingthe exhaust valve in preparation for the four-stroke process over again.

A cylinder naturally has only two strokes. To create the four strokes,valves are used that control the air entering and leaving the cylinder.The lobes 201 on the camshaft 202 determine the opening and closing ofthe valves, referred to as valve timing (see FIGS. 12 and 13).

The camshaft does not turn at the same rate as the crankshaft, since thevalves do not open and close with every cylinder stroke. Instead, thecamshaft is geared to turn at one-half the rate of the crankshaft.

FIG. 14 illustrates the push rod valve gear 203 and the overheadcamshaft 204. The push rod valve gear comprises a rocker 205, a tappetclearance 206, a camshaft which rotates at half of the engine speed(twice as many teeth as the sprocket) 207, a crankshaft sprocket 208, acam 209, another camshaft 210, a tappet 211, an inlet valve 212, anexhaust valve 213, a push rod 214, a spring 261, a lock nut foradjusting the valve clearance 262 and a rocker shaft 263. The overheadcamshaft 204 comprises a cam 264, a valve which is opened by therevolving cam 265, a camshaft 266, a camshaft sprocket 267, a buckettappet 268, a valve spring, a tensioner 270, a sprocket 271, anothertensioner 272, a crankshaft sprocket 273, an exhaust valve 274, an inletvalve 275, a valve spring 276, a bucket tappet 277, a sprocket, andanother camshaft 279.

Cylinder ID is defined as the process of determining at which stroke anengine's cylinder is. Because the valves, and not the cylinder position,determine the stroke, it is difficult to use the crankshaft angle totell in which stroke a cylinder is. From the crankshaft sensor we cantell when a cylinder is all the way up, but it is desirable to know ifit is in the compression stroke or the exhaust stroke.

When a cylinder is all the way up, it can be either in the compressionstroke, stroke 2, or in the exhaust stroke, stroke 4. Conversely, if acylinder is all the way down, it can be either in the intake stroke,stroke 1, or in the ignition stroke, stroke 3. Thus, although thecrankshaft angle can be used to identify the position of the cylinder,it is desirable to know if it is in the compression stroke or theexhaust stroke.

State-of-the-art engines without ionization sensors determine cylinderID from a special camshaft sensor and toothed wheel located on thecamshaft. This adds cost and complexity to an engine. In addition,because the sensor only indicates the position of one cylinder (forexample, top dead center TDC of cylinder one during compression), anengine crankshaft must rotate up to two times to identify its stroke,depending on its orientation when it came to a stop. FIG. 15 illustratesthe valve timing overlap of the four strokes on the engine crankshaft.In reality, the number of rotations is often more, since the mosttypical type of sensor (the Variable Reluctance Sensor) will not work atlow speeds and might be missed on the first rotation or two until thespeed reaches a minimum threshold. It is therefore desirable to be ableto use the ionization sensor to determine the cylinder ID very quicklyand to be able to eliminate the camshaft sensor and wheel.

In a Spark Ignition (SI) engine the spark plug is already inside of thecombustion chamber, and can be used as a detection device withoutrequiring the intrusion of a separate sensor. During combustion, a lotof ions are produced in the plasma. H₃O⁺, C₃H₃ ⁺, and CHO⁺ are producedby the chemical reactions at the flame front and have sufficiently longexciting time to be detected. If a bias voltage is applied across thespark plug gap, these free ions are attracted and will create a current.

An ionization detection setup 280 consists of a coil-on-plugarrangement, with a device in each coil to apply a bias voltage acrossthe tip when the spark isn't arcing. The current across the spark plugtip is isolated and amplified prior to being measured (see FIG. 16). Thecoils 281 (with ion detection) are attached to a module 282 (with ionprocessing).

A spark plug ionization signal measures the local conductivity at thespark plug gap when combustion occurs in the cylinder. The changes ofthe ionization signal versus crank angle can be related to differentstages of a combustion process. The ion current typically has threephases: the ignition or spark phase, the flame front phase, and thepost-flame phase. The ignition phase is where the ignition coil ischarged and later ignites the air/fuel mixture. The flame front phase iswhere the flame (flame front movement during the flame kernel formation)develops in the cylinder and consists, under ideal circumstances, of asingle peak. The current in the flame front phase has shown to bestrongly related to the air/fuel ratio. The post-flame phase depends onthe temperature and pressure development in the cylinder and generates acurrent whose peak is well correlated to the location of the peakpressure.

The ionization signal represents ionization current after ignition.During ignition, it represents the combined ignition current and ioncurrent (i.e., ionization current). This is because in the presentinvention, the ionization current and the ignition current flow in thesame direction. Before ignition, the ion signal represents the secondwinding current fluctuation caused by the charge current of the primarywinding.

FIG. 17 illustrates a typical ionization signal showing the pressure 283and ionization signals 284 for cylinder #1. The present method ofdetecting cylinder ID uses the spark phase of the signal. When the airin a cylinder is compressed, the resistance between the spark plugelectrodes will increase. This is because air is a natural insulator,with its own breakdown voltage based on a number of different factors(density, humidity, temperature, etc). This increased resistance willresult in a couple of discernable effects.

The duration of a spark (or spark duration) on a compression stroke willbe shorter than one without compression. It will take longer for thevoltage to build up before the spark arcs, and as the energy isdissipated, the spark will end sooner as the voltage drops. There areseveral problems with this method. The first is that it generallyrequires the use of edge detection to determine the spark duration,since sampling at a resolution of one sample/degree (typical) will notprovide sufficient accuracy to an event of this short duration,especially at lower engine speed. In addition, there are other variablesthat can contribute significant noise to this reading, especially sincethe difference in the duration of the spark is small enough that a goodsignal/noise ratio is useful.

The spark coils can be partially charged (instead of fully charging it)to a predetermined level. Next, a determination is made as to whichcoil(s) failed to fire or spark. The cylinders that failed to fire areon the compression stroke, because the resistance is high enough thatthe partially charged coils are unable to deliver the voltage requiredto break down the gas between the spark plug gap.

The increased resistance will also affect the secondary voltage peak. Ahigher secondary side voltage will be required to arc a spark across thegap. This can be measured on the primary side through the inducedcurrent flow. Problems with this method are that the IGBT (InsulatedGate Bipolar Transistor) generally used to turn on and off the primaryside current has voltage protection that inhibits voltages above 400V(typical). This can render this peak detection method of minimal use.

Therefore, an improved method of using the ionization current sensor todetermine cylinder ID is proposed. In one embodiment, the spark coilsare partially charged (instead of fully charged) to a predeterminedlevel. Next, the coils are observed to determine which coil(s) failed tofire. The cylinders that contain the coils that failed to fire are onthe compression stroke. The coils failed to fire because the gas mixtureis high enough that the partially charged coils are unable to deliverthe voltage required to break down the resistance at the spark plug gap.

Thus, this embodiment involves the determination of which cylinders toapply a spark to and when; dwell time calculation; and determination ofwhich cylinder is in compression by observing ionization current afterthe IGBT is turned off.

In another embodiment, the present invention involves the determinationof which cylinders to apply a spark to and when; calculation of thespark durations; and determination of which cylinder is in compression.

First, it is determined which cylinders to spark and when. This will becalibrated information specific for a particular engine. For a fourcylinder engine (shown in FIG. 18) with firing order (one, three, four,two), a determination where 0 degrees is on the crankshaft requires upto one full rotation of the engine crankshaft, until the missing tooth(typically used) is found. At that point, cylinders one and four aresparked at 0 degrees (their top dead center (TDC)-locations). If thedetermination fail (i.e., none of the spark coils fail to fire),cylinders three and two will be fired at 180 degrees to determine whichone is in compression. This would continue until the cylinder ID isdetermined.

The method is nearly identical for eight cylinder engines, except thatfour cylinders may be sparked simultaneously to increase the chances ofsuccessful detection. In four, six, and ten cylinder engines the processis similar, with pairs of cylinders being sparked at different crankangles. Three and five cylinder engines are slightly different in thatthe strokes on opposing cylinders are completely opposite. The resultswill be the same, since only one cylinder will misfire because it is attop dead center TDC of the compression stroke.

The calculation of the amount of energy used to charge the spark coilsis dependant upon a number of variables such as engine speed, load, etc.Applying too much energy may spark all cylinders, regardless of thestroke, and fail to detect the cylinder in compression. Too littleenergy may spark none of the cylinders, and fail to detect the cylinderin compression. Therefore proper spark energy level is used fordetecting the cylinder in compression. This is illustrated in FIGS. 19and 20.

The actual spark energy is related to the dwell time that is set for thespark plug timing. The higher the current that is flowing through thecoil, the higher the stored energy the coil will contain. When theengine control module ECU turns on the IGBT, the coil starts to charge.When the engine control module ECU turns off the IGBT, it createsinductive flyback, and the spark will occur if there is enough energy inthe coil to create the breakdown voltage. Because spark timing is fixed(IGBT off-time), the IGBT “on” time is the control (output) for thedwell calculation. During normal engine operation, the engine controlmodule ECU tries to calculate the IGBT turn on time such that the coilis fully charged by the time the spark occurs and the IGBT is thenturned off. If there is too much dwell time, energy is wasted and excessheat is generated in the coil. If there is too little dwell time, thecoil will not be fully charge, which may result in a misfire or partialburn due to a missing or degraded spark. Because the spark timing isimportant and shouldn't be changed, the ECU will tend to overcharge thecoil (too much dwell) to guarantee accurate spark timing.

As stated above, an ionization signal measures the local conductivity atthe spark plug gap when combustion occurs in the cylinder. The reason isthat as the gas in the cylinder is compressed during the compressionstroke, the gas density increases and the resistance of the gas tocurrent flow increases. Therefore, the resistance between the spark plugelectrodes increases.

Typically, 12 volts DC is applied for 1 msec to the primary winding ofthe ignition coil. This voltage is stepped up to more than 30 kVolts onthe secondary winding. This high voltage is required to break down theair gap between the spark plug gap and generate a spark arc. This isillustrated in FIG. 20 a. FIG. 20 a illustrates that the voltage isproportional to the coil current (sloped part of curve) until maximumcurrent is reached.

When a cylinder is compressed, the gas density between the spark plugelectrodes may be too high to generate an arc when the ignition coil isnot fully charged.

By varying the dwell time (the amount of time that the voltage isapplied to the primary coil), the available energy applied to the sparkplug electrodes is also varied. The shorter the dwell time, the less theavailable energy. As stated previously, the dwell time is controlled bythe “on” time of the IGBT.

The failure of a spark plug to spark is reflected in the ionizationsignal. That is, the ionization signal shows a sequence of pulses, seeFIG. 21, after dwell is completed, a ringing effect when the energystored in the secondary coil is consumed. Thus, the ionization signalcan be used to determine whether a cylinder is in compression stroke.The present method reduces the amount of dwell time used to charge acoil in a cylinder. Thus, the energy that will be applied across thespark plug electrodes will be reduced. The specific dwell time isselected so that the spark plug located in a cylinder that is not incompression will spark, while a spark plug in a cylinder that is incompression won't spark. In a preferred embodiment, the dwell time isreduced to between 30 to 50% of the typical 1 msec dwell time.

The present invention uses reduced dwell time (as compared to normalcoil charging). As is indicated by the following equation, the dwelltime is a function of several variables, each affecting the energyrequired to cause a spark to occur in a compressed cylinder:T _(on) =T _(off)−ƒ(ACT, ECT, MAP, N)

where T_(off) represents Spark Timing (the time the IGBT is turned off),ACT represents Air Charge Temperature, ECT represents Engine CoolantTemperature, MAP represents Manifold Air Pressure, and N representsEngine Crank Speed.

The spark timing is selected to maximize the gas density difference ofthe selected two cylinders to spark. Therefore, the best spark timingfor cylinder identification is at the TDC location of selected pair ofthe cylinders. For a four cylinder engine with firing order one, three,four, and two, the first pair (cylinders one and four) will be at thenext available crank degree of either zero or 360 crank degrees, and thesecond pair (cylinders three and two) will be at either 180 or 540 crankdegrees.

There are other factors, such as humidity, which also have an effect onthe process. Their effect is generally negligible. To reduce thecalibration burden, some variables may be eliminated in the abovecalculation, although the minimum necessary formula would be:T _(on) =T _(off)−ƒ(N)

In a preferred embodiment, which cylinder is in compression isdetermined by observing the ionization current after the IGBT is turnedoff, and determining whether a spark has occurred or not.

FIG. 21 illustrates the process of firing all the coils in the threecylinders of a three-cylinder engine near the cylinder one Top DeadCenter position when cylinder one is nearing the end of its compressionstroke. The top curve 285 represents cylinder #1 pressure. The bottomcurve represents all coils firing at the same time at each cylinderfiring 286, 287 and 288. This example is shown to display thedifferences between the cylinders in compression and those that are notin compression. Actual firing schemes will be the result of the engineconfiguration and were discussed above.

FIG. 22 displays the results, showing that two of the cylinders sparked(saturating the ionization current signal), while cylinder one didn'tbreak down due to lack of the higher voltage required, resulting in“ringing”. The dot-dash curve 286 represents cylinder one which had nospark due to higher gas density in compression stroke. The solid curve287 represents cylinder two, which sparked due to relatively low gasdensity (not in compression). The dash-dash curve 288 representscylinder three, which sparked due to relatively low air density (not incompression).

FIG. 22 also illustrates the difference between ionization signalsdetected from different cylinders. The secondary coil voltage ofcylinder one is not high enough to break down the gas gap and thevoltages of cylinders two and three breaks down their gas gaps. Forcylinder one, the gas between the spark plug gap was not broken down anda spark was not generated. The width of the first ionization pulse afterthe completion of dwell has a much shorter duration than the ionizationsignals of cylinders two and three. The ionization signals of cylinderstwo and three, where break-down occurred, have much longer pulse widths.Thus, by measuring the duration of the ionization signal pulses fromeach cylinder, one can detect which cylinder is in compression.

Those skilled in the art can immediately see a number of methods toprovide a yes/no answer to the question of whether a spark event hasoccurred, several of which are listed below.

In the case where ringing associated with the circuit does not causesaturation with the ion voltage/current levels that the microprocessoris measuring, it is possible to take a measurement during the expectedspark window. If the peak magnitude of the measured pulse sequence isgreater than a threshold, then a spark has occurred. Otherwise, a sparkhas not occurred. The reason is that the peak ringing current in thesecondary coil is relatively smaller than the spark current. FIG. 23illustrates a sampling method of determining whether a spark occurred.

If the ringing saturates, a method that doesn't depend on absolutemeasurement values is used. One method is to convert the current tovoltage, integrate the signal, and then use a comparator to determine ifthe integrated ionization signal over the spark window is above acertain threshold. If so, then a spark has occurred. Otherwise, a sparkhas failed to occur. FIG. 24 illustrates a spark energy integrationapparatus for determining whether a spark occurred, where the sparkenergy is defined as the integrated ionization voltage over the sparkwindow

An overall flowchart showing the logic used in determining whether aspark occurred in a cylinder is shown in FIG. 25. As shown in theflowchart of FIG. 26, the values from all ionization signals aredetected (340), filtered (345), and integrated (350). The integratedionization signal is then sampled and held (355) and compared with areference value (360). If the energy is below this reference, then nospark occurred (365, 370). If the integrated value in the cylinderexceeds a reference value or threshold, then a spark occurred (365,375). The energy is defined as the ionization voltage during ignitionintegrated over the ignition window. Typically, the spark energy can beapproximated by using the formula E=V²*(t/R), where E represents Energy,V_(ION) represents ionization voltage proportional to ionizationcurrent, R represents Resistance, and t represents time.

Since resistance R is assumed to be constant due to the ionizationmeasurement circuit, and it is known that the circuit saturates during aspark event, multiplying V_(max) ² by the time results in arepresentative figure. A typical figure might be (5V²)*0.5 msec, whichis proportional to the actual spark energy. The 0.5 msec represents atypical integration window at some engine speed (the actual windowvaries with engine speed), and the 5V represents the maximum value thatthe ionization measurement circuit produces. The typical reference valueor threshold is set at 75% of this energy. These steps are illustratedin the flowchart shown in FIG. 26.

Section D: A Method of Detecting Cylinder ID Using In-CylinderIonization to Measure Spark Duration

As discussed above, the cylinder (CID) detection process involves thecalculation of spark timing from the ion signal. The procedure ofdetermining which cylinders to spark and when is unchanged with respectto the procedure disclosed in Section C. FIG. 27 illustrates allmultiple cylinders being sparked at a given location on the crankshaft,where only one cylinder is actually in compression. The broad curve 289represents cylinder #1 pressure. The narrow curve 290, 291, 292 whichpasses through the broad curve at around the 321K sample represents allcoils firing near top dead center TDC of each cylinder. The spark withthe shortest duration is the cylinder under compression.

FIG. 28 shows a close-up of the resulting spark durations, as relayed bythe ionization voltage proportional to ionization current. It is clearthat one of the three cylinders has a much shorter duration. This is thecylinder under compression. Note the “ringing” effect after the sparksend, which complicates detection efforts slightly. The dash-dash curve290 represents cylinder one which had the shortest spark duration. Thedot-dash curve 291 represents cylinder two which had a longer sparkduration. The solid curve 292 represents cylinder three which had alonger spark duration.

It is clear that a factor used to determine which cylinder is incompression is linked to the ability to measure the duration of thespark. Two methods used to time this duration are described below.

First, it is possible to use edge detection techniques to determine theamount of spark duration. Shown in FIG. 29 is a case where a timer 400is turned on and off by the rising and falling edges of the spark eventas seen through an ionization circuit. An ionization signal 100 and awindow signal 410 are input to a rising edge detector 415 and a fallingedge detector 420. The rising and falling edges toggle a flip-flop 425operably connected to the enable pin of the timer 400. Note that sincethere is “ringing” in the circuit after the spark event, in a preferredembodiment the edge detectors 415, 420 used are one-shot. The outputs ofmultiple timing circuits would be held in a sample and hold circuit 430and compared to see which event was shortest in duration. A clock signal405 drives the timer 400 and flip-flop 425. FIG. 30 is a flowchart ofthe steps used when determining spark duration using edge detection

A different method for timing the spark duration would be to integratethe ionization signal. The circuit with the least amount of integratedenergy would be the cylinder in compression. FIG. 31 illustrates acomparator circuit 440 using integration to compare two cylindersignals. The energy from two ionization signals 100 _(S1), 100 _(S2) aredetected (500), integrated (510) in integrators 1 and 2 (445, 450) andcompared (520). The result is sampled and held (530). The switch 455 andthe memory circuit 460 together act as a sample and hold circuit 462,which is triggered by the window signal 410. The comparator 440 is usedto indicate which of the two signals 100 _(S1) or 100 _(S2) is higher.The cylinder in compression would output the signal with the loweramount of energy. The energy is proportional to the ionization voltageduring ignition integrated over the ignition window. These steps areillustrated in the flowchart shown in FIG. 32.

Section E: Ignition Coil with Integrated Coil Driver and IonizationDetection Circuitry

Internal Combustion Engine (ICE) on-plug ignition coils with transistordrivers located in ECMs or other remote locations are prone to high EMIemissions and are subject to interference from other components due tolong connecting wires. Ionization detection circuits have even greaterEMI problems because of their very low signal current levels(microamperes). The solution is to integrate both the coil drivertransistor and ionization detection circuits into the on-plug ignitioncoil (FIG. 33).

In a preferred embodiment, parts rated at 140 degrees centigrade areused in both the coil driver transistor and the ionization detectioncircuit which are integrated into the coil package to addresstemperature and thermal shock concerns. Additionally, parts rated at 20Gare used in both the coil driver transistor and the ionization detectioncircuit to address vibration concerns.

By placing the circuit on top of the coil or on the side of the coil,the connection distance from the circuit to the secondary winding isminimized (see FIGS. 33 a and 33 b for the top of the coil embodiment).Thus, the circuit is less susceptible to noise. Another advantage isthat the placement is easy to assemble. The driver and ion circuit boardsimply clips on to the ignition coil assembly. Therefore, use of clipconnectors 65 is another advantage provided by the layout. The top view33 a illustrates the cover 60 used to protect the driver and ionizationcircuit board 10 and the connector 50 operably connected to thepowertrain control module PCM. The side view 33 b illustrates primarywinding 16, the core 13, the secondary winding 18, the driver andionization circuit board 10, the clip connector 65, the cover 60, theconnector 55 operably connected to the spark plug, and the connector 50which is operably connected to the powertrain control module PCM. InFIG. 34, the circuit is placed on the side of the coil. The ionizationsignal 100, gate drive signal Vin, ground Gnd, power B+, coil primaryfeed 16 and coil secondary 18 inputs located on a printed wire board 70are illustrated. The power B+, ground Gnd, gate drive Vin and ionizationsignal 100 signals are also located on four connector blades 71.

Section F: A Method for Reducing Pin Count of an Integrated IgnitionCoil with Driver and Ionization Detection Circuit by MultiplexingIonization and Coil Charge Current Feedback Signals

The combustion process of a spark ignited (SI) engine is governed byin-cylinder air/fuel (A/F) ratio, temperature and pressure, exhaust gasrecirculation (EGR) rate, ignition time, duration, etc. Engine emissionand fuel economy are tightly dependent on its combustion process. Forhomogenous combustion engines, most often, the engine A/F ratio iscontrolled in a closed loop using a heated exhaust gas oxygen (HEGO) oruniversal exhaust gas oxygen (UEGO) sensor. The exhaust gasrecirculation EGR rate is controlled with the help of Δ pressuremeasurement. Due to unavailability of a low cost combustion monitorsensor, engine spark timing is controlled in an open loop and correctedby knock detection result. One of the low cost options for combustionsensing is ionization detection, which measures ion current generatedduring the combustion process by applying a bias voltage onto a sparkplug gap. When moving the ignition driver on to the ignition coil (e.g.,pencil and on-plug coils), it would be desirable to integrate both theignition driver circuit and ionization detection circuit onto theignition coil, see Section E of this application for details. One openissue is to use minimum pin count of the integrated package to coverboth integrated driver and ionization detection circuits for reducedcost. This feature proposes to multiplex the ignition coil chargecurrent feedback signal with the ionization signal, and therefore,reduce the package pin count by one.

The conventional design for an integrated ignition coil with driver andionization detection circuit consists of five pins: coil charge gatesignal, charge current feedback signal, ionization current signal,battery power and ground. Each pin count increases ignition subsystemcost due to the ignition coil connector, the harness, and the enginecontrol unit (ECU) connector. In order to reduce subsystem cost, thisinvention multiplexes both the primary charge current feedback and theionization current signals. This is possible because the primary coilcharge and combustion events occur sequentially.

It is desirable to integrate the ignition coil driver electronics ontothe ignition coil (e.g., pencil or coil-on-plug), see Section E, mainlyto get rid of high current pins between powertrain control module PCMand ignition coils and to reduce electrical and magnetic interference. Adesign for an integrated ignition coil with driver consists of fourpins: Ignition coil primary winding charge gate signal; Primary windingcharge current feedback signal; Battery power supply B+; and Batteryground.

With the integration of an ionization detection circuit onto theignition coil with integrated driver, an additional output pin isrequired to send the detected ionization current signal back to thepowertrain control module PCM. Therefore, the ignition coil withintegrated driver and ionization circuit requires a five-pin connector.

In order to reduce cost and make coil packaging easier, this inventionproposes to multiplex both the ionization and driver current feedbacksignals into one signal so that the ignition coil with integrated driverand ionization circuit has the same pin count number as the driver oncoil design.

FIG. 35 shows a diagram of an integrated coil driver and ionizationdetection sub-system 72 which illustrates multiplexing the ionizationsignal and the charge current or driver current feedback signals. Thesub-system consists of a coil driver circuit 75, an ionization detectioncircuit 80, and an amplifier 85. The driver circuit 75 charges theprimary winding 16 of the ignition coil 12 when the charge is enabled.Next, the ionization detection circuit 80 applies a bias voltage throughthe secondary winding 18 of the ignition coil 12 to the spark plug 14and the resulting ionization current I_(ion) is due to the ions producedduring the combustion process. The amplifier 85 magnifies the detectedsignal for improved signal to noise ratio.

FIGS. 36 a-c shows the charge command V_(in) signal (FIG. 36 a), thedetected ionization voltage or signal 100, represented by a dashed line,and the charge current feedback signal 102, represented by a solid line(FIG. 36 b), and the ionization voltage or signal multiplexed with thecharge current feedback signal 106 (FIG. 36 c). Between t₀ and t₁ thereis no combustion and the ignition coil 12 is at rest. The charge commandV_(in) becomes enabled at t₁ and disabled at t₂. During this period, theprimary coil 16 is fully charged (600). This is a detection window forcurrent feedback. The ignition of the air/fuel mixture occurs betweentime t₂ and time t₃ (610). The combustion process is completed betweentime t₃ and time t₄ (620).

The feasibility of multiplexing both the charge current feedback andionization detection signals is shown in FIG. 36 b. Since combustion 620happens after ignition 610, the main ionization detection window occursbetween time t₂ and time t₄. This sequencing of events makes it possibleto multiplex both the ionization signal 100 and the charge currentfeedback signal 102.

In the present method, the multiplexed signal 106 first outputs theionization detection signal 100 and replaces the ionization signal 100with the charge current feedback signal 102 when the charge commandV_(in) is enabled, see FIG. 36 a. FIG. 36 b shows both charge currentfeedback 102 (solid) and ionization 100 (dash) signals. FIG. 36 c showsthe multiplexed signal 106.

During time t₀ and time t₁, the output is ionization signal 100. Theswitch SW1 is connected to the output of the ionization detectioncircuit (or the ion current node) 82. When the charge command V_(in) isenabled between t₁ and t₂, the switch SW1 switches to the charge currentfeedback signal node 84 which is connected through driver circuit 75 toone end of the primary winding 16 of the ignition coil 12. Thus, theswitch SW1 outputs the charge current feedback signal 102 (a voltagesignal across resistor 24 that is proportional to primary chargecurrent, see FIG. 35). After t₂, the signal 106 switches back toionization signal 100. Note that between t₂ and t₃, the ionizationsignal 100 provides information regarding ignition process 104, i.e.,the ignition current detected by the ion circuit, and between t₃ and t₄information regarding combustion process (630).

FIG. 37 shows a diagram of an integrated coil driver and ionizationdetection sub-system. The sub-system consists of ignition coil 12 and anionization detection circuit 28, 30. A driver circuit charges theprimary winding 16 of the ignition coil 12 when the charge is enabledVin. Next, the ionization detection circuit 28, 30 applies a biasvoltage through the secondary winding 18 of the ignition coil 12 to thespark plug 14. Ionization current is generated due to the ions producedduring the combustion process. An amplifier is used to magnify thedetected signal for improved signal to noise ratio.

In summary, the multiplexed feedback signal 106 outputs the ionizationfeedback signal 100 and switches to charge current feedback signal 102when the charge command V_(in) is active. FIG. 38 is a flowchartillustrating the steps of the present embodiment of the integrated coildriver and ionization detection sub-system 72.

Section G: A Device to Provide a Regulated Power Supply for In-CylinderIonization Detection by Using the Ignition Coil Fly Back Energy andTwo-Stage Regulation

This feature pertains to a device that provides a regulated power supplyfor in-cylinder ionization detection by harvesting the excess ignitioncoil leakage and magnetizing energy immediately following the turn offof the ignition coil IGBT. Spark ignition systems for internalcombustion engines must deliver sufficient energy to a spark plugelectrode air gap to ignite the compressed air-fuel mixture in thecylinder. To accomplish this, energy is stored in a magnetic devicecommonly referred to as an ignition coil 12. The stored energy is thenreleased to the spark plug 14 air gap at the appropriate time to ignitethe air-fuel mixture. A schematic diagram of a typical ignition coil isshown in FIG. 39. The coil 12, which is actually a flyback transformer,consists of primary 16 and secondary windings 18 that are magneticallycoupled via a highly permeable magnetic core 13. The secondary winding18 normally has many more turns than the primary winding 16. This allowsthe secondary voltage to fly up to very high levels during the “flyback”time.

Energy is stored in the coil by turning on a power switch, normally anInsulated Gate Bipolar-Junction Transistor (IGBT) 22, and applyingbattery voltage across the primary winding 16 of the ignition coil 12.With a constant voltage applied to the primary inductance (L_(pri)),primary current (I_(pri)) increases linearly until it reaches apredetermined level (FIGS. 40 and 41).

The energy stored in the coil is a square function of the coil primarycurrent per the following equation:Energy=½×L _(pri)×(I _(pri))²

Once the primary current I_(pri) has reached a predetermined peak level,the primary power switch IGBT 22 is turned off. When this occurs, theenergy stored in the coil inductance L_(pri) causes the transformerprimary voltage to reverse and fly up to the IGBT clamp voltage,nominally 350 to 450 volts. Since the secondary winding 18 ismagnetically coupled to the primary winding 16, the secondary voltagealso reverses, rising to a value equal to the primary clamp voltagemultiplied by the secondary to primary turns ratio (typically 20,000 to40,000 volts). This high voltage appears across the electrodes of thespark plug 14, causing a small current to flow between the spark plug 14electrodes through the electrode air gap. Though this current is small,the power dissipated in the air gap is significant due to the highvoltage across the air gap. The power dissipated in the electrode airgap rapidly heats the air between the electrodes causing the moleculesto ionize. Once ionized, the air/fuel (A/F) mixture between theelectrodes conducts heavily, dumping the energy stored in the flybacktransformer 12 in the spark plug 14 air gap (FIG. 42). The suddenrelease of energy stored in the flyback transformer 12 ignites theair/fuel (A/F) mixture in the cylinder.

In-cylinder ionization detection requires a regulated power supply toestablish a bias voltage across the spark plug 14 electrodes. Thisvoltage, which is generally in the 80 to 100 volt DC range, produces anionization current I_(ion) that is nominally limited to a few hundredmicro-amps. The resulting ionization current I_(ion) is then sensed andamplified to produce a usable signal for diagnostic and controlpurposes.

Since the magnitude of the ionization current I_(ion) is relativelysmall, it is desirable to locate the sensing and amplifying electronicsclose to the coil 12 and spark plug 14. It is also preferable to locatethe high voltage power supply very close to the ionization electronicssince bussing high voltages under a car hood is undesirable. Therefore,means are provided to create the high voltage locally.

One method of creating the ionization potential is to use a DC—DCconverter to create an 80 to 100 volt power supply from the available 12Volts DC at the ignition coil 12. This method, though straight forwardand reliable, requires several components to implement and, therefore,may be cost and space prohibitive.

Another method is to charge a capacitor from the collector of theprimary IGBT immediately following IGBT 22 turn off. The primary benefitof this technique is that it does not require a separate boost converterto create the ionization bias voltage. A second, and perhaps equallysignificant benefit is that it captures at least part of the energystored in the transformer leakage inductance and transfers it to theenergy storage capacitor. Normally, this energy would be dissipated onthe IGBT 22 as heat, raising its operating temperature. An embodiment ofthis technique is shown schematically in FIG. 43. As previouslydescribed, the energy stored in the coil inductance L_(pri) causes thetransformer primary voltage to reverse and fly up to the IGBT clampvoltage (350 to 450 volts) when the IGBT 22 turns off. When this occurs,diode D1 is forward biased allowing a current to flow through D1 and thecurrent limiting resistor R1 into capacitor C1. Zener diode D2 limitsthe voltage on C1 to approximately 100 volts.

A disadvantage of this method is that the energy storage capacitor, C1,stores energy at a relatively low voltage (100 volts) compared to themagnitude of the flyback voltage (approximately 400 volts). Since theenergy stored in the capacitor C1 is a function of the square of thecapacitor voltage, storing energy at a low voltage requires a muchhigher value of capacitance for a given amount of stored energy than ifthe capacitor was allowed to charge to a higher voltage. For example, tostore 500 μ-joules at 100 volts requires a 0.1 μfd capacitor. To storethe same energy at 200 volts requires only a 0.025 μfd capacitor. Thecapacitance is reduced by a factor of four by doubling the capacitorvoltage.

A second disadvantage of this method is that the R1×C1 time constantmust be short enough to allow a complete recharge of C1 in the shorttime between IGBT 22 turn off and spark plug firing (normally less thana micro-second). At the same time, C1 must be large enough to supplyionization current I_(ion) without a substantial drop in the voltage onC1 under worst-case conditions (low rpm, fouled spark plug). This forcesR1 to be a relatively small value (10's of ohms) and results in arelatively large capacitor charging current when the IGBT 22 turns off.Under nominal operating conditions (2000 to 3000 rpm, clean spark plug)the discharge on C1 due to ionization is moderate resulting in excesscharging current being diverted into the zener diode (D2). The productof excess zener diode current and zener voltage constitutes energywasted in the zener diode D2.

Another method is to charge an energy storage capacitor with thesecondary ignition current by placing the capacitor in series with thesecondary winding 18 of the flyback transformer 12. An embodiment ofthis technique is shown schematically in FIG. 44. Spark current flowingin the secondary 18 of the ignition coil 12 charges the energy storagecapacitor C1 via diode D1. Once the voltage on C1 reaches the zenervoltage, secondary current is diverted through the zener diode D1,limiting the voltage on C1 to approximately 100 volts.

Since C1 is in series with the secondary winding, it is not possible toharvest leakage energy to charge C1. A portion of the energy which wouldnormally be delivered to the spark gap is now stored in C1. Therefore,the stored magnetizing energy in the transformer 12 must be increased tocompensate for this energy diversion.

A method according to the present invention provides a regulated powersupply for in-cylinder ionization detection by harvesting the excessignition coil leakage and magnetizing energy in a manner which is moreeffective than the previously described techniques. FIG. 45 is aschematic diagram of the circuit that employs this method. At firstglance, the circuit appears to be similar to the second circuitdescribed supra in which an energy storage capacitor is charged from theprimary winding (FIG. 43). There are novel and unobvious differences,however, that allow this new circuit to perform the energy storage andvoltage regulation function in a fundamentally different and moreeffective manner.

One difference is the addition of energy storage capacitor, C2, whichreplaces capacitor C1 as the primary energy storage device. As shown inFIG. 46, one terminal of capacitor C2 is connected to the cathode of D1and the other terminal of capacitor C2 is connected to ground. Energy isstored in the coil by turning on a power switch (IGBT) 22, and applyingbattery voltage across the primary winding 16 of the ignition coil 12(700). When the switch (IGBT) 22 turns off, the energy stored in thecoil leakage and magnetizing inductances causes the transformer primaryvoltage to reverse. The collector voltage of the IGBT 22 increasesrapidly until it exceeds the voltage on capacitor C2 by one diode drop,0.7 Volts. At this point, diode D1 forward biases, allowing a forwardcurrent to flow through D1 into capacitor C2 (FIG. 46). When thisoccurs, energy that is stored in the transformer leakage inductance istransferred to capacitor C2 instead of being dissipated on the IGBT(710). Some transformer magnetizing energy may be transferred tocapacitor C2 as well.

R1, which is now a much larger value (100's of kohms), is sized tosupply enough current from the high voltage capacitor reservoir (C2) tosatisfy the average ionization current requirements, and to provideadequate bias current to voltage regulator diode, D2. Because resistorR1 is such a large value, there is never a large excess current flow inD2. This significantly reduces the energy wasted on the voltageregulator diode compared to the other techniques previously described.

When the spark plug 14 fires, the secondary voltage collapses and themagnetizing energy stored in the transformer is delivered to the sparkgap to ignite the air-fuel mixture in the cylinder. Simultaneously, theprimary voltage collapses, reverse biasing D1 and ending the charging ofcapacitor C2. At this time, C2 is at its maximum voltage, typically 350to 400 volts. Capacitor C2 now acts as the primary energy reservoir tomaintain the charge on capacitor C1 while supplying current to theionization circuits and the voltage regulator diode D1 (720).

Capacitor C2 is sized such that it can supply average ionization currentunder worst case conditions (600 rpm, fouled spark plug) whilemaintaining a sufficiently high voltage to regulate the ionizationsupply bus voltage at 100 volts (730) to lower voltage capacitor C1.Since capacitor C1 is no longer the primary energy storage element, itneed only be large enough to limit the voltage drop on the ionizationbus to acceptable levels while supplying transient ionization currents.Steady state currents are supplied by C2. The discharge current paths ofC2 are shown in FIG. 47.

In a preferred embodiment, C1 and C2 equal 0.1 uF and R1 equals 1.8Megohms. Rsense equals 40 milliohms. C1 is rated at 630 volts. Theforward voltage drop for D1 is 0.7 Volts, while the avalanche voltagefor zener diode D2 is 100 Volts. D1 is rated at 800 volts reversevoltage.

Thus, the present invention uses a two step method for charging theionization detection circuit, as opposed to just one stage. Capacitor C2is charged first, typically up to 400 Volts DC. C2 is then used as areservoir to charge the second stage capacitor C1. Capacitor C1 willtypically charge up to 100 Volts DC. This two stage method of chargingproduces a stable 100 volt output at capacitor C1. In the prior art, thevoltage of capacitor C1 varies as energy is removed. In addition, byusing two capacitors or stages, more energy is available to theionization detection circuit.

FIG. 48 is a flowchart which illustrates the steps taken in the presentembodiment of a circuit that provides a regulated power supply forin-cylinder ionization detection by harvesting excess ignition coilleakage and magnetizing energy.

Non-limiting examples of some of the unique features of the IonizationDetection Bias Circuit include: (1) capturing all of the energy storedin the transformer leakage inductance and using it as an energy sourcefor the ionization electronics circuits; (2) reducing the dissipationand resulting heating of the primary IGBT by diverting the leakageenergy into the high voltage capacitor instead of allowing it to bedissipated on the IGBT; (3) storing energy at a high voltage to takeadvantage of the fact that energy stored in a capacitor increases as thesquare of the capacitor voltage allowing a physically smaller capacitorto be used to achieve the same stored energy; (4) reducing the energywasted on the voltage regulator diode by increasing the value of thecurrent limiting resistor such that the diode never sees large reversecurrents; and (5) reducing the value of C1 to reflect the fact that C1is no longer the main energy storage element for the ionizationelectronics and that C1 need only be large enough to limit the voltagedrop on the ionization voltage bus to acceptable levels duringionization current transients.

Section H: A Method for Reducing Pin Count of an Integrated IgnitionCoil with Driver and Ionization Detection Circuit by MultiplexingIonization Current, Coil Charge Current Feedback, and Driver GateSignals

This feature of the present invention addresses many of the deficienciesnoted in the discussion set forth above in Section F entitled “A methodfor Reducing Pin Count of an Integrated Ignition Coil with Driver andIonization Detection Circuit by Multiplexing Ionization and Coil ChargeFeedback Signals.” This feature of the invention multiplexes theignition driver gate signal with both the ignition coil charge currentfeedback signal and the ionization signal, and therefore, reduces thepackage pin count by two.

The conventional design for an integrated ignition coil with driver andionization detection circuit consists of five pins: 1) coil charge gatesignal, 2) charge current feedback signal, 3) ionization current signal,4) battery power, and 5) battery ground. Each additional pin increasesignition subsystem cost due to the connections to the ignition coilconnector, the harness, and the engine control module (ECU) connector.In order to reduce subsystem cost, this invention multiplexes theignition charge gate signal with both the primary charge currentfeedback and the ionization current signals. Therefore, the presentinvention has the following pin count: 1) battery power, and 2) batteryground, and 3) multiplexed coil charge gate signal, charge currentfeedback signal, and ionization current signal.

It is a goal to integrate the ignition coil driver electronics onto theignition coil (e.g., pencil or coil-on-plug). In order to reduce orremove high current pins between the powertrain control module (PCM) andthe ignition coil, a design for an integrated ignition coil with driverconsists of four pins: an Ignition coil primary winding charge gatesignal, a Primary winding charge current feedback signal, a Batterypower supply B+, and a Battery ground.

With the integration of an ionization detection circuit onto theignition coil with an integrated driver, an additional output pin isrequired to send the detected ionization current signal back to thepowertrain control module PCM. Therefore, the ignition coil with anintegrated driver and an ionization circuit requires a five-pinconnector.

In order to reduce cost and make coil packaging easier, this feature ofthe invention multiplexes the ignition primary charge gate signal withboth the ionization and the driver current feedback signals so that theignition coil with an integrated driver and an ionization circuit has apin count number as few as three.

FIG. 49 shows a diagram of an integrated coil driver with driver andionization detection sub-system 90. The integrated ignition coilsub-system 90 consists of a coil driver circuit 75, an ionizationdetection circuit 80, dual amplifiers 85, 86, and a gate signalregeneration circuit 92. The ignition coil has a primary 16 and asecondary winding 18. Since the two amplifiers 85, 86 are identicalcurrent sources, the voltage difference between the two inputs of thedifference comparison circuit 93 reflects the charge gate signal V_(in)assuming resistance R4 is equal to the sum of resistors R2 and R3. Whenthe difference is greater than a given threshold, the output 108 ofdifference comparison circuit 93 remains high, generating a primarycharge gate signal V_(in). The driver circuit 75 charges a primarywinding 16 of an ignition coil 12 when the charge command signal V_(in)is enabled. The ionization detection circuit 75 applies a bias voltagethrough a secondary winding 18 of the ignition coil 12 to the spark plug14. A resulting ionization current ion is generated due to the ionsproduced during the combustion process. Finally, the top amplifier 85magnifies the detected signal for improved signal to noise ratio.

FIG. 50 illustrates multiplexing the ionization, the charge gate and thecurrent feedback signals. FIG. 50 shows the charge gate signal Vin(solid line) and the differential comparison gate signal command 108(dashed line) (FIG. 50 a), the detected ionization signal 100 (dashedline) and the charge current feedback signal 102 (solid line) (FIG. 50b), and the differential ionization signal (ionization signalmultiplexed with the charge current feedback signal 106, see FIG. 50 c).Between times to and to there is no combustion and the ignition coil 12is at rest. The switch SW1 is connected to the ionization current node82 and outputs the ionization current I_(ion) through the top amplifier85 to P_(IN) 1. The output of the top amplifier 85 is also connected toa first input of a difference comparison circuit 93. It is seen fromFIG. 49 that the node pin 1 connected to the output of the top amplifier85 acts as an output node P_(IN) 1 for the ion current signal and thecharge current feedback signals 102. The powertrain control module PCMcharge gate signal V_(in) becomes enabled at time t₁ and disabled attime t₂. At this time, charge gate current Ig flows from the charge gatesignal generator 92 through resistor R3 to ground causing gating voltageto appear at a second input of the difference comparison circuit 93.

The reason that this happens is that the charge gate signal generator 92is a current source. The current flows through resistor R3 becauseresistor R2 is much greater than resistor R3. Thus the voltage V_(Ig)appearing at the junction of resistors R2 and R3 is R3(Ig). The voltageappearing at the output node of the top amplifier 85 isV2=I1(R2+R3)+R3(Ig), where I1 is either the ionization signal 100 or thecharge current feedback signal 102. The voltage appearing acrossresistor R4 is V1=I1(R2+R3), where R4 was selected to equal R2+R3. In apreferred embodiment, R4=180 ohms, R2=150 ohms and R3=30 ohms.

In a preferred embodiment, the difference comparison circuit 93 is acomparator with two inputs and one output. The difference between thetwo input signals is V2−V1=R3(Ig) (800). Its function is to apply thecharge command signal 108 to the coil driver circuit 75 (810). Due tothe additional current applied at R3 when the powertrain control modulePCM charge gate signal V_(in) becomes enabled, the voltage differencebetween R4 and R3 is large enough so that the output 108 of thedifference comparison circuit 93 remains high during this period, andthe primary coil 16 charges fully (820). When the gate command signalV_(in) is not activated, V1=V2=I1(R2+R3) and the output of thedifference comparison is low. Thus, although two pins have beeneliminated, the charge gate signal V_(in) can still be used to chargethe coil 12. In addition, the time period t₁ to t₂ is a detection windowfor current feedback.

The air/fuel mixture is ignited between times t₂ and t₃ (830), and thecombustion process is completed between times t₃ and t₄ (840). Thefeasibility of time multiplexing between the charge current feedback andionization signals is shown in FIG. 50 b. The switch SW1 switches itsinput from the ionization current node 82 to a charge current feedbacknode 84 which is connected to one end of a primary winding 16 of theignition coil 12 through the coil driver circuit 75. Since combustionhappens after ignition, the main ionization detection window is betweent₂ and t₄. This make it possible to multiplex both the ionization signal100 and the charge current feedback signal 102. The multiplexed signal106 outputs the ionization detection signal and replaces the ionizationsignal 100 with the charge current feedback signal 102 when the chargecommand Vin is enabled, see FIG. 50 c. FIG. 50 b shows both chargecurrent feedback and ionization signals, and FIG. 50 c shows themultiplexed signal. During times t0 and t1, the output multiplexedsignal 106 is the ionization signal 100. When the charge command isenabled between times t₁ and t₂, the output switches to the chargecurrent feedback signal 102 (a voltage signal proportional to primarycharge current) see FIG. 50 c. After time t₂, the multiplexed signal 106switches back to the ionization signal 100. Note that between times t₂and t₃, the ionization signal 100 provides information regarding theignition process, and between t₃ and t₄ information regarding thecombustion process (850).

In summary, the multiplexed signal 106 outputs the ionization signal 100and switches to charge current feedback signal 102 when the chargecommand is active, i.e., between times t₁, and t₂.

FIG. 51 is a flowchart disclosing the steps taken with the presentembodiment of the integrated coil driver and ionization detectionsub-system 90 in which package pin count by two.

Section J: A Device for Reducing the Part Count and Package Size of anIn-Cylinder Ionization Detention System by Integrating the IonizationDetection Circuit and Ignition Coil Driver into a Single Package

Note that the Section I designation has been intentionally not includedin this application.

Ignition coil control is currently realized using an IGBT residinginside of a powertrain control module (PCM). Biasing the secondary side18 of the ignition coil 12 with a predetermined voltage and reading thevarying level of current flowing between the electrodes of the sparkplug 14 accomplishes ionization detection. The level of current flow islow requiring the signal to be amplified. The electronics for ionizationdetection can reside either inside the powertrain control module PCM orin a separate module outside of the powertrain control module PCM. Twoembodiments are disclosed, an ASIC and a single electronic package. TheASIC defined within this disclosure integrates the IGBT and theionization detection electronics into one silicon device. The singleelectronic package defined within this disclosure combines the IGBT andthe ionization detection electronics in discrete form into oneelectronic package.

The following describes two embodiments of an integrated ionizationdetection circuit and ignition coil driver according to the presentinvention, an ASIC and a single electronic package. The devicesdescribed within this disclosure reduce the cost and complexity of anin-cylinder ionization detection system by combining like functionalityinto one ASIC or electronic module easing packaging constraints.

Ionization detection is accomplished by biasing the secondary side 18 ofthe ignition coil 12 with a predetermined voltage and reading thevarying level of current flowing through the secondary coil 18 and sparkplug 14 circuit. The level of current flow is low therefore requiringamplification to increase the noise immunity of the signal. Thecircuitry used to bias the coil 12 and accomplish the amplification ismade up of devices that can easily be placed into silicon.

One advantage of packaging the circuit on one piece of silicon is thatthe properties of silicon allow for the creation of “smart” IGBTs thatcan return a current proportional to the current flowing across the IGBTwithout creating the heat of sense resistors. A second advantage is thatthe current signal can also be scaled to match the ionization currentsignal allowing them to be passed back as one signal.

The Ignition Control Ion Sense ASIC (ICIS) device is a combination ofthe ionization detection circuitry 80 and the ignition control circuitry75 into one ASIC. The ionization detection circuitry 80, composed ofdevices that can be duplicated in silicon, combined with the alreadyavailable “smart” IGBT silicon designs creates ICIS in one silicondevice. This includes single chip as well as multiple chip (chip on chipor chip by chip) solutions. ICIS can be located within the powertraincontrol module PCM, outside of the powertrain control module PCM as aseparate module (see DICIS), or in/on the ignition coil 12.

The Discrete Ignition Ion Sense package (DICIS) is a combination of theionization detection circuitry 80 and the ignition control circuitry 75into one electronic package. The ionization detection circuitry 80, inits discrete form, combined with either a “smart” IGBT, “dumb” IGBT, or“dumb” IGBT with additional control and protection creates DICIS in oneelectronic package. This includes single substrate as well as multiplesubstrate designs. DICIS can be located in/on the ignition coil 12, nearthe ignition coil 12, or in other package friendly locations within thevehicle.

FIG. 35 illustrates a circuit which has only 4 pins and which allows thecharge current feedback signal 102 and the ionization signal 100 to bepassed back as one signal on one pin through the use of timemultiplexing.

FIGS. 52 and 53 are logic block diagrams of the present invention forboth the ASIC (ICIS) (FIG. 52) and the single electronics packageoptions (DICIS) (FIG. 53). Shown in both FIGS. 52 and 53 is the coildriver circuit 75 comprising a current sink 94, protection limitationU1, amplifier U2, and a base IGBT 22. In addition an ionization detector80 comprising current mirror 30, power supply 20 and capacitor 28 isshown. Also shown are resistors 24 and 44, spark plug 14, ignition coil12 with primary winding 16 and secondary winding 18, amplifier U3, andanalog multiplexer buffer 86. The current sink 94 removes noise in theform of voltage spikes. The voltage spikes are high voltage, but ofshort duration. The current sink prevents these spikes from turning onthe IGBT. However, the current sink 94 allows the IGBT command signal topass.

FIG. 54 is a circuit diagram of a current sink 94.

ASIC Option

The Ignition Control Ion Sense ASIC (ICIS) package 81 features anintegral IGBT driver, IGBT driver control, and ion sensing currentfeedback circuitry. All the active circuitry is contained in one silicondevice integrated into the ignition coil. The ICIS ASIC can be placed onthe coil, near the coil, or within the powertrain control module PCM inplace of the current coil driver IC.

The combustion monitoring coil (CMC) has a four pin interface: 1)Power—B+, 2) Control (V_(IN))—Controls IGBT on/off and the source of thecurrent feedback signal, 3) Current Feedback (100, 102, 106)—When IGBTis on, indicates coil current. When IGBT is off, indicates ion current,and 4) Ground.

Single Electronics Package Option

The Discrete Ignition Control Ion Sense (DICIS) package 83 features anintegral IGBT driver and ion sensing current feedback. All the activecircuitry is discrete and contained in one electronic package. Thepackage can be placed on the coil or near the coil.

The combustion monitoring coil (CMC) has a four pin interface: 1)Power—B+; 2) Control—(V_(IN)) Controls IGBT on/off and the source of thecurrent feedback signal; 3) Current Feedback (100, 102, 106)—when IGBTis on, indicates coil current—when IGBT is off, indicates ion current;and 4) Ground.

Section K: A Device to Provide a Regulated Power Supply for in CylinderIonization Detention by Using a Charge Pump

The ionization current of an internal combustion engine can be used fordiagnosing engine misfire, knock, ignition timing and duration, etc.Through sophisticated signal conditioning processing, the individualcylinder combustion properties can also be obtained. Therefore, theengine combustion process can be precisely monitored and controlled inclosed loop. To detect in-cylinder ions generated during the combustionprocess, a DC bias voltage needs to be applied between the spark pluggap. There are two ways to generate the DC bias: conventional DC powersupply (large electronics) and capacitor charges by primary or secondaryflyback voltage (high voltage capacitor). Both approaches can not meetthe requirement to integrate the ionization circuit on the ignition coil(see Section E) due to the size of DC power supply and reliability ofhigh voltage capacitors. This feature of the invention uses a highvoltage charge pump to provide enough DC bias voltage for measuringionization current.

Typically, flyback voltage is used to charge the capacitor whichsupplies current to the ionization detection circuit, see Section G.This necessitates the use of high voltage capacitors. Generally, ceramiccapacitors are used. However, as temperature fluctuates, the board onwhich the capacitor is mounted can flex, causing the ceramic capacitorto crack and fail. In the present invention, the ionization current biasvoltage source is a charge pump, see FIG. 55.

FIG. 55 shows an example of ionization detection circuit 80 with ablow-up bias voltage circuit using a charge pump 98. The charge pumpcircuit 98 converts the 12 Volt DC at the B+ terminal to a 90 to 100volt pulse train with a pulse repetition frequency of 500 Hz at thecharge pump output 99.

In a preferred embodiment, a model number MIC4827 EL driver (U5) is usedin the charge pump circuit 98. It is manufactured by Micrel. Thefollowing table provides the pin configuration of the chip (U5) alongwith a table explaining their functions.

Pin Pin Number Name Pin Function 1 VDD Supply (input): 1.8 V to 5.5 Vfor internal circuitry. 2 RSW Switch Resistor (external Component): Setswitch frequency of the internal power MOSFET by connecting an externalresistor to VDD. Connecting the external resistor to GND disables theswitch oscillator and shuts down the device. 3 REL EL Resistor (ExternalComponent): Set EL frequency of the internal H-bridge driver byconnecting an external resistor to VDD. Connecting the external resistorto GND disables the EL oscillator. 4 GND Ground Return. 5 SW Switch Node(Input): Internal high-voltage power MOSFET drain. 6 CS Regulated BoostOutput (External Component): Connect to the output capacitor of theboost regulator and connect to the cathode of the diode. 7 VB EL Output:Connect to one end of the EL lamp. Polarity is not important. 8 VA ELOutput: Connect to the other end of the EL lamp. Polarity is notimportant.

The MIC4827 EL driver (U5) is comprised of two stages: a boost stage andan H-bridge stage. The boost stage steps the input voltage up to +90Volts. The MIC4827 features separate oscillators for the boost-andH-bridge stages. External resistors independently set the operatingfrequency for each stage.

In a preferred embodiment, capacitor C_(IN)=10 uF, capacitorC_(OUT)=0.033 uF/100 Volts, D3 is a model 1N4148 diode, L1 is a 220 uHinductor, resistor R7=322 kohms and resistor R6=3.32 Mohms.

Using a charge pump 98 as the DC bias voltage has several advantages.First, eliminating high voltage capacitors as the power supply for theion bias voltage (see Section G) leads to reduced cost and improvedreliability (avoids cracked capacitor in hash environment). Further,size reduction results in more available space that is helpful for bothpencil and COP (coil-on-plug) coils. Additionally, the capacitor biasvoltage, when charged by fly-back voltage (see Section G), requiresseveral ignition events to fully charge the capacitor. Also, in order tobe able to detect ionization current during engine start-up operation, afew ignitions are used to charge the capacitor and get the ionizationbias voltage ready. Using a charge pump can eliminate this requirement.Still further, since a charge pump can be easily manufactured on a pieceof silicon along with the rest of ionization detection circuit (seeSection E), this feature presents a large cost savings when comparedwith using expensive high voltage compact capacitors.

While the invention has been disclosed in this patent application byreference to the details of preferred embodiments of the invention, itis to be understood that the disclosure is intended in an illustrativerather than in a limiting sense, as it is contemplated that modificationwill readily occur to those skilled in the art, within the spirit of theinvention and the scope of the appended claims and their equivalents.

1. An integrated ignition system, comprising: an ignition coilcomprising a primary winding with a first and a second end and asecondary winding with a first and a second end; a coil driver circuithaving a first end operably connected to said second end of said primarywinding; an ionization detection circuit having at least two inputs andan output, wherein a first input is operably connected to said secondend of said primary winding, and a second input is operably connected tosaid first end of said secondary winding; a switch having at least twoinputs and an output, wherein a first input is operably connected tosaid output of said ionization detection circuit, a second input isoperably connected to a second end of said coil driver circuit, wherebysaid output of said switch is multiplexed between an ionization signaland a charge current feedback signal; and an ignition plug operablyconnected between said second end of said secondary winding and ground.2. The integrated ignition system according to claim 1 furthercomprising an amplifier having an input and an output, wherein saidinput is operably connected to said output of said switch.
 3. Theintegrated ignition system according to claim 2, wherein said integratedignition system further comprises: a charge gate input pin operablyconnected to a command input of said coil driver circuit; a ground pin;a battery supply pin operably connected to said first end of saidprimary winding; and an output pin operably connected to said output ofsaid amplifier.
 4. The integrated ignition system according to claim 1,wherein said ionization detection circuit comprises: a capacitor havinga first end operably connected to said second end of said primarywinding; and a current mirror having a first terminal operably connectedto said first end of said secondary winding and a second terminaloperably connected to said first end of said capacitor.
 5. A method ofdetecting an ionization signal and a driver current feedback signal,comprising the step of multiplexing the ionization signal and the drivercurrent feedback signal, wherein said step of multiplexing theionization signal and the driver current feedback signal comprises thesteps of: outputting the ionization signal; charging an ignition coil byenabling a charge command; outputting the charge current feedback signalwhile a charge command signal is enabled; disabling said charge commandsignal; igniting an air/fuel mixture; outputting an ignition currentsignal; combusting said air/fuel mixture; outputting said ionizationsignal; and combining said ionization signal, said charge currentfeedback signal and said ignition current signal.
 6. The methodaccording to claim 5 wherein said step of combining said ionizationsignal, said charge current feedback signal and said ignition currentsignal comprises outputting said ionization signal, said charge currentfeedback signal and said ignition current signal on a same output pin.7. The method according to claim 5 wherein said step of outputting acharge current feedback signal while said charge command signal isenabled comprises switching between said ionization signal and saidcharge current feedback signal when said charge command signal isenabled.
 8. A method of detecting an ionization signal and a drivercurrent feedback signal, comprising the step of multiplexing theionization signal and the driver current feedback signal, wherein saidstep of multiplexing the ionization signal and the driver currentfeedback signal comprises the steps of: outputting an ionization signal;enabling a charge command signal, whereby a primary winding of anignition coil is charged; outputting a charge current feedback signalwhile said charge command is enabled; disabling said charge commandsignal; and outputting said ionization signal after said charge commandsignal is disabled.
 9. An integrated ignition system, comprising: anignition coil comprising a primary winding having a first and a secondend and a secondary winding having a first and a second end; a coildriver circuit having a first end operably connected to said second endof said primary winding; a difference comparator having an outputoperably connected to an input of said coil driver circuit; anionization detection circuit having at least two inputs and an output,wherein a first input is operably connected to said second end of saidprimary winding, and a second input is operably connected to said firstend of said secondary winding; a switch having at least two inputs andan output, wherein a first input is operably connected to said output ofsaid ionization detection circuit, a second input is operably connectedto a second end of said coil driver circuit, whereby said output of saidswitch is multiplexed between an ionization signal and a charge currentfeedback signal; a first amplifier having an input and an output,wherein said input is operably connected to said output of said switchand said output is operably connected to a first input of saiddifference comparator; a second amplifier having an input and an output,wherein said input is operably connected to said output of said switchand said output is operably connected to a second input of saiddifference comparator; an ignition plug operably connected between saidsecond end of said secondary winding and ground; and a charge gatesignal generator having an output operably connected to said output ofsaid first amplifier.
 10. The integrated ignition system according toclaim 9 further comprising: a first resistor operably connected betweensaid output of said first amplifier and said output of said charge gatesignal generator; a second resistor operably connected between saidoutput of said charge gate signal generator and ground; and a thirdresistor operably connected between said output of said second amplifierand ground.
 11. The integrated ignition system according to claim 10wherein said ionization detection circuit comprises: a capacitor havinga first end operably connected to said second end of said primarywinding; and a current mirror having a first terminal operably connectedto said first end of said secondary winding and a second terminaloperably connected to said first end of said capacitor.
 12. Theintegrated ignition system according to claim 10 wherein said coildriver circuit comprises a switch operably connected between said secondend of said primary coil and ground.
 13. The integrated ignition systemaccording to claim 10 wherein said integrated ignition system furthercomprises: a ground pin; a battery power supply pin operably connectedto said first end of said primary coil; and an output pin operablyconnected to said output of said first amplifier.
 14. A method ofdetecting an ionization signal and a driver current feedback signal,comprising the step of multiplexing a charge command signal, theionization signal and the driver current feedback signal, wherein saidstep of multiplexing a charge command signal, the ionization signal andthe driver current feedback signal comprises the steps of: outputting anionization signal; enabling a charge command signal, whereby a primarywinding of an ignition coil is charged; generating a gating voltage byflowing charge gate current across a first resistor; generating a secondvoltage by outputting an ionization signal across said first resistorand a second resistor; comparing said gating voltage and said secondvoltage; outputting a charge command signal if said gating voltage isgreater than said second voltage; outputting a charge current feedbacksignal while said charge command is enabled; disabling said chargecommand signal; and outputting said ionization signal after said chargecommand signal is disabled.
 15. The method according to claim 14 whereinsaid step of outputting a charge current feedback signal while saidcharge command signal is enabled comprises switching between saidionization signal and said charge current feedback signal when saidcharge command signal is enabled.
 16. The method according to claim 14wherein said step of outputting said ionization signal after said chargecommand signal is disabled comprises switching between said chargecurrent feedback signal and said ionization signal when said chargecommand signal is disabled.
 17. The method according to claim 14 whereinsaid ionization signal and said charge current feedback signal areoutput on a same output pin.